Transparent electronics is an emerging technology for the realization of invisible devices and circuits for the next generation of optoelectronic devices and other electronics involving printing, large areas, low cost, flexibility, wearability, and fashion and design
Central to the realization of transparent electronics is the development of transparent thin-film transistors (TTFTs). Of interest to current research are the performance metrics including high device mobility and low temperature fabrication. Generally, high device mobility enables fast device operation and low power consumption, which broadens the application area of TTFTs. The low temperature fabrication of transparent devices on flexible substrates enables emerging applications such as e-paper, wearable displays, smart tags, and artificial skin “e-skin.” Low temperature fabrication of TTFTs can also lower the fabrication expense.
Traditionally, wide band-gap semiconductors were studied for TTFTs, such as GaN and oxide semiconductor films. However, TTFTs fabricated in these cases usually exhibit rather moderate mobilities. For instance, reported TTFTs fabricated using In—Ga—Zn—O film have shown a device mobility of ˜80 cm2V−1s−1 on glass substrates and ˜9 cm2V−1s−1 on polyethylene terephthalate (PET) substrates. In addition reported TTFTs with In2O3 films coupled with an organic dielectric layer exhibited mobility of 120 cm2V−1S−1 on glass substrates.
Recently, semiconductor nanowires have emerged as another class of materials that can be used to fabricate TTFTs. For example, transparent transistors using In2O3 nanowires have shown a mobility of 514 cm2V−1s−1 (see “Fabrication of Fully Transparent Nanowire Transistors for Transparent and Flexible Electronics” by S. Y. Ju et al., Nat. Nanotechnol., vol. 2, pp 378-384, 2007)
Despite the above-mentioned success, the reported mobility values are still low compared to non-transparent devices, indicating further room for improvement.
In addition, the oxide based TTFTs have generally been limited to n-type transistors. Indeed, the development of high performance transparent p-type transistors, which is an essential element in CMOS, still remains a great challenge.
To realize high-performance p-type TTFTs with high mobility, single-walled carbon nanotubes (SWNTs) may be a promising candidate for their intrinsic mobility of over 100,000 cm2V−1s−1, good mechanical flexibility, and good optical transparency. In addition, carbon nanotube devices usually exhibit p-type transport behavior, which complements the n-type oxide-based TTFTs.
In recent years, random nanotube networks were used as active channels for TTFTs. However the best obtained mobility was reported to be ˜30 cm2V−1s−1.
Thus, research continues to be conducted in order to achieve elements not only capable of high device mobility and low temperature fabrication, but also capable of integration and complementary circuitry.